Physical layer protocol data unit directional transmission

ABSTRACT

A method for transmitting a first physical layer (PHY) protocol data unit (PPDU) in a wireless local area network (WLAN) communication channel is described. One or more sectors of a service coverage area of a first communication device that are busy with a first transmission over the WLAN communication channel are identified. A second communication device is selected, using the identification of the one or more busy sectors, to receive the first PPDU during a second, directional transmission that at least partially temporally overlaps a duration of the first transmission. The first PPDU is generated for transmission to the second communication device. The first PPDU is transmitted to the second communication device as the second, directional transmission during the first transmission.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/778,602, entitled “Sector Based Association of STAwith AP,” filed on Dec. 12, 2018, which is hereby incorporated herein byreference in its entirety.

FIELD OF TECHNOLOGY

The present disclosure relates generally to wireless communicationsystems, and more particularly to concurrent transmissions in differentsectors.

BACKGROUND

Wireless local area networks (WLANs) have evolved rapidly over the pastdecade, and development of WLAN standards such as the Institute forElectrical and Electronics Engineers (IEEE) 802.11 Standard family hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughput, such as throughputs in the tens of Gbps range.In some scenarios where access points are located near each other, theirrespective service coverage areas spatially overlap and concurrenttransmissions from, or to, the access points may interfere with eachother. This interference prevents a second transmission from beingstarted by one access point once a first transmission has been startedby the other access point, until the first transmission has completed.

SUMMARY

In an embodiment, a method for transmitting a first physical layer (PHY)protocol data unit (PPDU) in a wireless local area network (WLAN)communication channel includes: identifying, at a first communicationdevice, one or more sectors of a service coverage area of the firstcommunication device that are busy with a first transmission over theWLAN communication channel; selecting, at the first communication deviceand using the identification of the one or more busy sectors, a secondcommunication device to receive the first PPDU during a second,directional transmission that at least partially temporally overlaps aduration of the first transmission; generating, at the firstcommunication device, the first PPDU for transmission to the secondcommunication device; and transmitting, at the first communicationdevice, the first PPDU to the second communication device as the second,directional transmission during the first transmission.

In another embodiment, an apparatus for transmitting a first PPDU in aWLAN communication channel includes a network interface device havingone or more integrated circuits. The one or more integrated circuitsinclude a sector controller configured to identify one or more sectorsof a service coverage area of a first communication device that are busywith a first transmission over the WLAN communication channel. Thesector controller is further configured to select, using theidentification of the one or more busy sectors, a second communicationdevice to receive the first PPDU during a second, directionaltransmission that at least partially temporally overlaps a duration ofthe first transmission. The one or more integrated circuits areconfigured to generate the first PPDU for transmission to the secondcommunication device. The one or more integrated circuits are configuredto transmit the first PPDU to the second communication device as thesecond, directional transmission during the first transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) having a first access point configured to transmit or receive aphysical layer (PHY) protocol data unit (PPDU) while anothertransmission is ongoing, according to an embodiment;

FIG. 2 is a diagram of an example access point of FIG. 1 configured toprovide a first service coverage area that overlaps with a secondservice coverage area of a second access point, according to anembodiment;

FIG. 3 is a diagram of an example access point of FIG. 1 configured forfull duplex communication using directional transmissions, according toan embodiment;

FIG. 4 is a diagram of an example access point of FIG. 1 configured forparallel communication using directional transmissions, according to anembodiment;

FIG. 5 is a block diagram of the access point of FIG. 4, in anembodiment;

FIG. 6 is an example timing diagram for an access point of FIG. 1configured to request a frame exchange for channel estimation, in anembodiment; and

FIG. 7 is a flow diagram illustrating an example method for transmittinga PPDU, in an embodiment.

DETAILED DESCRIPTION

In various embodiments described below, a first access point isconfigured to transmit (or receive) a physical layer (PHY) protocol dataunit (PPDU) while another transmission is ongoing. In some embodimentsand/or scenarios, the other transmission is between a second accesspoint that has a service coverage area that overlaps with a servicecoverage area of the first access point. In other embodiments and/orscenarios, the other transmission is from, or to, the first accesspoint. The first access point is configured to identify one or moresectors within its service coverage area that are busy with the othertransmission. The access point selects a second communication device(e.g., a client station associated with the access point) to receive thePPDU (or to transmit the PPDU) using the one or more busy sectors. In anembodiment, for example, the access point selects the secondcommunication device so that the busy sectors are avoided during thetransmission of the PPDU. In another embodiment, for example, the accesspoint selects the second communication device so that co-channelinterference with the second access point is reduced. The access pointtransmits the PPDU as a second, directional transmission, for example,towards a sector in which the selected second communication device islocated. In various embodiments, the directional transmission isperformed using one or more of directional antennas, semi-directionalantennas, and phased arrays.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 110 configured to utilize sectors within a service coverage area,according to an embodiment. The WLAN 110 includes an access point (AP)114 that comprises a host processor 118 coupled to a network interfacedevice 122. The network interface device 122 includes one or more mediumaccess control (MAC) processors 126 (sometimes referred to herein as“the MAC processor 126” for brevity) and one or more physical layer(PHY) processors 130 (sometimes referred to herein as “the PHY processor130” for brevity). The PHY processor 130 includes a sector controller132 and a plurality of transceivers 134, and the transceivers 134 arecoupled to a plurality of antennas 138. Although three transceivers 134and three antennas 138 are illustrated in FIG. 1, the AP 114 includesother suitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 134 andantennas 138 in other embodiments. In some embodiments, the AP 114includes a higher number of antennas 138 than transceivers 134, andantenna switching techniques are utilized.

In various embodiments, the AP 114 is configured to provide service forthe WLAN 110 (e.g., for a basic service set) within a service coveragearea, for example, service coverage area 230 (FIG. 2). In someembodiments, the AP 114 includes at least some directional antennas(e.g., parabolic antenna, grid antenna) and/or or semi-directionalantennas (e.g., patch/panel antenna, Yagi antenna) that are configuredto transmit and/or receive signals in a portion of a service coveragearea provided by the AP 114. In some embodiments, the AP 114 includes atleast some antennas configured as a phased array. In still otherembodiments, the AP 114 includes one or more of omnidirectionalantennas, semi-directional antennas, directional antennas, and phasedarray antennas. In various embodiments, the AP 114 is configured todivide its service coverage area into a plurality of sectors and toassign ones of the antennas 138 to ones of the plurality of sectors.

The network interface device 122 is implemented using one or moreintegrated circuits (ICs) configured to operate as discussed below. Forexample, the MAC processor 126 is implemented, at least partially, on afirst IC, and the PHY processor 130 is implemented, at least partially,on a second IC, in various embodiments. As another example, at least aportion of the MAC processor 126 and at least a portion of the PHYprocessor 130 are implemented on a single IC. For instance, the networkinterface device 122 is implemented using a system on a chip (SoC),where the SoC includes at least a portion of the MAC processor 126 andat least a portion of the PHY processor 130.

In an embodiment, the host processor 118 includes a processor configuredto execute machine readable instructions stored in a memory device (notshown) such as a random access memory (RAM), a read-only memory (ROM), aflash memory, etc. In an embodiment, the host processor 118 isimplemented, at least partially, on a first IC, and the networkinterface device 122 is implemented, at least partially, on a second IC,in various embodiments. As another example, the host processor 118 andat least a portion of the network interface device 122 is implemented ona single IC.

The network interface device 122 is configured to generate and transmitdifferent PHY protocol data units (PPDUs), in various embodiments and/orscenarios. In some embodiments, the network interface device 122transmits different PPDUs concurrently using different antennas. In someembodiments, for example, the network interface device 122 is configuredto transmitting a first PPDU as a directional transmission duringanother transmission, as described herein.

In various embodiments, the MAC processor 126 and/or the PHY processor130 of the AP 114 are configured to generate data units, and processreceived data units, that conform to a WLAN communication protocol suchas a communication protocol conforming to the IEEE 802.11 Standard oranother suitable wireless communication protocol. For example, the MACprocessor 126 is configured to implement MAC layer functions, includingMAC layer functions of the WLAN communication protocol, and the PHYprocessor 130 is configured to implement PHY functions, including PHYfunctions of the WLAN communication protocol. For instance, the MACprocessor 126 is configured to generate MAC layer data units such as MACservice data units (MSDUs), MAC protocol data units (MPDUs), etc., andprovide the MAC layer data units to the PHY processor 130. The PHYprocessor 130 is configured to receive MAC layer data units from the MACprocessor 126 and encapsulate the MAC layer data units to generate PHYdata units such as PHY protocol data units (PPDUs) for transmission viathe antennas 138. Similarly, the PHY processor 130 is configured toreceive PHY data units that were received via the antennas 138, andextract MAC layer data units encapsulated within the PHY data units. ThePHY processor 130 may provide the extracted MAC layer data units to theMAC processor 126, which processes the MAC layer data units.

PHY data units are sometimes referred to herein as “packets,” and MAClayer data units are sometimes referred to herein as “frames.”

In connection with generating one or more radio frequency (RF) signalsfor transmission, the PHY processor 130 is configured to process (whichmay include modulating, filtering, etc.) data corresponding to a PPDU togenerate one or more digital baseband signals, and convert the digitalbaseband signal(s) to one or more analog baseband signals, according toan embodiment. Additionally, the PHY processor 130 is configured toupconvert the one or more analog baseband signals to one or more RFsignals for transmission via the one or more antennas 138.

In connection with receiving one or more RF signals, the PHY processor130 is configured to downconvert the one or more RF signals to one ormore analog baseband signals, and to convert the one or more analogbaseband signals to one or more digital baseband signals. The PHYprocessor 130 is further configured to process (which may includedemodulating, filtering, etc.) the one or more digital baseband signalsto generate a PPDU.

The PHY processor 130 includes amplifiers (e.g., a low noise amplifier(LNA), a power amplifier, etc.), a radio frequency (RF) downconverter,an RF upconverter, a plurality of filters, one or more analog-to-digitalconverters (ADCs), one or more digital-to-analog converters (DACs), oneor more discrete Fourier transform (DFT) calculators (e.g., a fastFourier transform (FFT) calculator), one or more inverse discreteFourier transform (IDFT) calculators (e.g., an inverse fast Fouriertransform (IFFT) calculator), one or more modulators, one or moredemodulators, etc.

The PHY processor 130 is configured to generate one or more RF signalsthat are provided to the one or more antennas 138. The PHY processor 130is also configured to receive one or more RF signals from the one ormore antennas 138.

The MAC processor 126 is configured to control the PHY processor 130 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 130, andoptionally providing one or more control signals to the PHY processor130, according to some embodiments. In an embodiment, the MAC processor126 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a readROM, a flash memory, etc., to provide at least some of the functionalitydescribed herein. In another embodiment, the MAC processor 126 includesa hardware state machine that provides at least some of thefunctionality described herein.

The sector controller 132 is configured to divide the service coveragearea into the plurality of sectors and assign ones of the antennas 138to ones of the plurality of sectors, in various embodiments. In anembodiment, the sector controller 132 includes, or is communicativelycoupled with, one or more carrier sense components 133 (or energydetector components) configured to determine whether a WLANcommunication channel is busy or idle, for example, by measuring asignal strength within the WLAN communication channel. In an embodiment,ones of the carrier sense components 133 are configured to measure thesignal strength in particular sectors or directions. Although the sectorcontroller 132 is shown as part of the PHY processor 130, the sectorcontroller 132 is a separate controller or processor within the networkinterface 122, in other embodiments. In some embodiments, the carriersense components 133 are included within the transceivers 134, insteadof within the sector controller 132.

In an embodiment, the MAC processor 126 and the PHY processor 130 areconfigured to operate according to a first WLAN communication protocol(e.g., an IEEE 802.11 be Standard, or extremely high throughput (EHT)),and also according to one or more second WLAN communication protocols(e.g., as defined by one or more of the IEEE 802.11n Standard, IEEE802.11ac Standard, the IEEE 802.11ax Standard and/or other suitable WLANcommunication protocols) that are legacy protocols with respect to thefirst WLAN communication protocol. The one or more second WLANcommunication protocols are sometimes collectively referred to herein asa “legacy WLAN communication protocol” or simply “legacy protocol.”

The WLAN 110 includes a plurality of client stations 154. Although threeclient stations 154 are illustrated in FIG. 1, the WLAN 110 includesother suitable numbers (e.g., 1, 2, 4, 5, 6, etc.) of client stations154 in various embodiments. The client station 154 includes a hostprocessor 158 coupled to a network interface device 162. The networkinterface device 162 includes one or more MAC processors 166 (sometimesreferred to herein as “the MAC processor 166” for brevity) and one ormore PHY processors 170 (sometimes referred to herein as “the PHYprocessor 170” for brevity). The PHY processor 170 includes a pluralityof transceivers 174, and the transceivers 174 are coupled to a pluralityof antennas 178. Although three transceivers 174 and three antennas 178are illustrated in FIG. 1, the client station 154 includes othersuitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 174 andantennas 178 in other embodiments. In some embodiments, the clientstation 154 includes a higher number of antennas 178 than transceivers174, and antenna switching techniques are utilized. In some embodiments,one or more of the network interface device 162, the MAC processor 166,and the PHY processor 170 are configured similarly to the networkinterface device 122, the MAC processor 126, and the PHY processor 130,respectively.

The network interface device 162 is implemented using one or more ICsconfigured to operate as discussed below. For example, the MAC processor166 is implemented on at least a first IC, and the PHY processor 170 isimplemented on at least a second IC, in various embodiments. As anotherexample, at least a portion of the MAC processor 166 and at least aportion of the PHY processor 170 is implemented on a single IC. Forinstance, the network interface device 162 is implemented using an SoC,where the SoC includes at least a portion of the MAC processor 166 andat least a portion of the PHY processor 170.

In an embodiment, the host processor 158 includes a processor configuredto execute machine readable instructions stored in a memory device (notshown) such as a RAM, a ROM, a flash memory, etc. In an embodiment, thehost processor 158 is implemented, at least partially, on a first IC,and the network device 162 is implemented, at least partially, on asecond IC, in various embodiments. As another example, the hostprocessor 158 and at least a portion of the network interface device 162is implemented on a single IC.

In various embodiments, the MAC processor 166 and the PHY processor 170of the client device 154 are configured to generate data units, andprocess received data units, that conform to the WLAN communicationprotocol or another suitable communication protocol. For example, theMAC processor 166 is configured to implement MAC layer functions,including MAC layer functions of the WLAN communication protocol, andthe PHY processor 170 is configured to implement PHY functions,including PHY functions of the WLAN communication protocol. The MACprocessor 166 is configured to generate MAC layer data units such asMSDUs, MPDUs, etc., and provide the MAC layer data units to the PHYprocessor 170. The PHY processor 170 is configured to receive MAC layerdata units from the MAC processor 166 and encapsulate the MAC layer dataunits to generate PHY data units such as PPDUs for transmission via theantennas 178. Similarly, the PHY processor 170 is configured to receivePHY data units that were received via the antennas 178, and extract MAClayer data units encapsulated within the PHY data units. The PHYprocessor 170 may provide the extracted MAC layer data units to the MACprocessor 166, which processes the MAC layer data units. In someembodiments, for example, the MAC processor 166 is configured similarlyto the MAC processor 126. In an embodiment, for example, the MACprocessor 166 includes multiple instances of the multi-band backofftimers 127.

The PHY processor 170 is configured to downconvert one or more RFsignals received via the one or more antennas 178 to one or morebaseband analog signals, and convert the analog baseband signal(s) toone or more digital baseband signals, according to an embodiment. ThePHY processor 170 is further configured to process the one or moredigital baseband signals to demodulate the one or more digital basebandsignals and to generate a PPDU. The PHY processor 170 includesamplifiers (e.g., an LNA, a power amplifier, etc.), an RF downconverter,an RF upconverter, a plurality of filters, one or more ADCs, one or moreDACs, one or more DFT calculators (e.g., an FFT calculator), one or moreIDFT calculators (e.g., an IFFT calculator), one or more modulators, oneor more demodulators, etc.

The PHY processor 170 is configured to generate one or more RF signalsthat are provided to the one or more antennas 178. The PHY processor 170is also configured to receive one or more RF signals from the one ormore antennas 178.

The MAC processor 166 is configured to control the PHY processor 170 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 170, andoptionally providing one or more control signals to the PHY processor170, according to some embodiments. In an embodiment, the MAC processor166 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a ROM,a flash memory, etc. to provide at least some of the functionalitydescribed herein. In an embodiment, the MAC processor 166 includes ahardware state machine that provides at least some of the functionalitydescribed herein.

In an embodiment, the MAC processor 166 and the PHY processor 170 areconfigured to operate according to the first WLAN communicationprotocol, and also according to the legacy WLAN communication protocol.

In an embodiment, each of the client stations 154-2 and 154-3 has astructure that is the same as or similar to the client station 154-1.Each of the client stations 154-2 and 154-3 has the same or a differentnumber of transceivers and antennas. For example, the client station154-2 and/or the client station 154-3 each have only two transceiversand two antennas (not shown), according to an embodiment.

In an embodiment, one or both of the client stations 154-2 and 154-3 areconfigured to operate according to the legacy WLAN communicationprotocol, but not according to the first WLAN communication protocol.Such client stations are referred to herein as “legacy client stations.”Similarly, an access point that is similar to the AP 114 and isconfigured to operate according to the legacy WLAN communicationprotocol, but not according to the first WLAN communication protocol, isreferred to herein as a “legacy AP.” More generally, wirelesscommunication devices that are configured to operate according to thelegacy WLAN communication protocol, but not according to the first WLANcommunication protocol, are referred to herein as a “legacycommunication devices.”

FIG. 2 is a diagram of an example access point (AP) 220 configured toprovide a service coverage area 230 that overlaps with a servicecoverage area 212 of another AP 210, according to an embodiment. The AP220 is referred to herein as a “second AP” and generally corresponds tothe access point 114 of FIG. 1, in an embodiment. The access point 210is referred to herein as a “first AP” and corresponds to the accesspoint 114 of FIG. 1, or another suitable communication device. In someembodiments, the first AP 210 is a “legacy” access point that does notprovide sector-based features (e.g., directional transmissions tosectors).

The second AP 220 includes a plurality of antennas 222 configured fordirectional transmissions to sectors while another transmission isongoing. In the embodiment shown in FIG. 2, the second AP 220 comprisesfour directional antennas 222-1, 222-2, 222-3, and 222-4 configured tosend and receive in different sectors 232-1, 232-2, 232-3, and 232-4,respectively. In some embodiments, the antennas 222 generally correspondto antennas 138 of the AP 114 in FIG. 1. Although four directionalantennas are shown, in other embodiments, the AP 220 has a differentconfigurations of antennas, for example, sixteen omnidirectionalantennas configured as four separate phased arrays having four antennaseach. In an embodiment, the plurality of antennas 222 are configured toform a plurality far field radiation sectors or antenna patterns thatare substantially non-overlapping.

The second AP 220 includes a sector controller (e.g., sector controller132) configured to divide the service coverage area 230 into a pluralityof sectors, for example, sectors 232-1, 232-2, 232-3, and 232-4, and toassign ones of the antennas 222 to the different sectors. The second AP220 is configured to perform directional transmissions to clientstations according to a sector in which the client stations are located,in various embodiments. In some scenarios, the directional transmissionreduces co-channel interference with other communication devices, forexample, the AP 210 or a client station 214, even when the othercommunication devices are performing a first transmission using sameWLAN radio resources (i.e., same channel bandwidth).

The service coverage area 230 is a geographical area covered by thesecond AP 220, in an embodiment. In other words, the service coveragearea 230 is an area in which a client station is able to authenticateand associate with the second AP 220. In the embodiment shown in FIG. 2,the sectors 232 are illustrated as non-overlapping with each other andgenerally rectangular in shape for ease of description; however,respective sizes and shapes of the sectors 232 are variable and maydepend, for example, on environmental factors such as walls, furniture,objects or people moving throughout the service coverage area 230, orother factors. In some embodiments, the size and shape of the sectors232 depends upon an orientation of one or more corresponding antennas.In some embodiments, the sector controller 132 determines the sectors232 such that at least some of the sectors partially spatially overlap,for example, at boundaries between adjacent sectors. In some scenarios,overlapping the boundaries reduces the likelihood of a client stationbeing within a “dead zone” having reduced received signal strength fromthe second AP 220.

In the embodiment shown in FIG. 2, the first AP 210 provides a servicecoverage area 212 that at least partially spatially overlaps the servicecoverage area 230 of the second AP 220. In various embodiments and/orscenarios, the first AP 210 performs a first transmission 214 of a PPDU(e.g., a data frame) to the client station 214 (STA1) and the clientstation 214 performs a second transmission 216 of a PPDU (e.g., anacknowledgment to the data frame) to the first AP 210. The firsttransmission 214 and the second transmission 216 cause interference 224and 226, respectively, at the second AP 220; however, the interference224 and 226 are generally located within the sectors 232-2 and 232-3,while other sectors are not affected or less affected (e.g., sectors232-1 and 232-4).

The second AP 220 is configured to identify one or more sectors of theservice coverage area 232 that are busy, for example, busy with thefirst transmission 214 and/or the second transmission 216, in variousembodiments. In an embodiment, the sector controller 132 of the secondAP 220 uses the carrier sense component 133 to identify particularsectors that are busy. By using sectorization, the second AP 220 isconfigured to consider each sector of the service coverage area 230 as aseparate carrier sense opportunity so that when a signal is received ina first sector (e.g., from a client station or another access point),another sector can be used by the AP 220 for a different transmission.In the embodiment shown in FIG. 2, the carrier sense component 133identifies the sector 232-2 and the sector 232-3 as busy, based on thereceived interference 224 and 226.

The second AP 220 is configured to select another communication deviceassociated with the AP 220, for example, among the client stations 240and 250, to receive a PPDU during a directional transmission that atleast partially temporally overlaps a duration of an ongoingtransmission (i.e., the transmissions 214 and/or 216). The second AP 220selects the other communication device using the identification of theone or more busy sectors, for example, to avoid transmission in thosebusy sectors.

The second AP 220 is configured to maintain respective target lists ofsectors of the service cover area 230 in which respective ones ofcommunication devices associated with the second AP 220 are estimated tobe located, in various embodiments. In the embodiment shown in FIG. 2,for example, the second AP 220 maintains i) a first target list for theclient station 214 that includes the sector 232-3, ii) a second targetlist for the client station 240 that includes the sector 232-4, and iii)a third target list for the client station 250 that includes the sector232-1 and the sector 232-2. In some embodiments, the second AP 220includes both sectors 232-1 and 232-2 in the target list for the clientstation 250 because the location of the client station 250 is adjacentto both sectors. In some embodiments, for example, where sectors atleast partially spatially overlap, the second AP 220 includes bothsectors when the location of the client station 250 is within bothsectors. Although only one or two sectors are included in the targetlists in the description, the target lists include three, four, or moresectors in other embodiments, for example. In some embodiments, thesecond AP 220 provides the corresponding target list, or an indicationthereof, to the client stations. In other embodiments, the second AP 220maintains the target lists without sharing its contents with the clientstations (for example, when the client stations do not explicitlysupport sectorization).

The second AP 220 estimates the sector in which the client station islocated during an authorization and association procedure, in anembodiment. In an embodiment, for example, the second AP 220 transmits(e.g., broadcasts) a beacon frame and performs the location estimationbased upon respective energy detectors associated with the antennas 222when receiving a response to the beacon frame. In an embodiment, thesecond AP 220 broadcasts the beacon frame by transmitting the beaconframe by an omnidirectional antenna. In another embodiment, the secondAP 220 broadcasts a copy of the beacon frame in each sector of theservice coverage area 230. In some embodiments, the second AP 220 isconfigured to update the target list corresponding to a client stationbased on a reception of a PPDU having a non-null data portion (e.g., adata frame), for example, based on received signal strength of the PPDUat multiple antennas of the second AP 220.

In some scenarios, the second AP 220 performs the directionaltransmission concurrently with the ongoing transmission and thusimproves overall efficiency of the WLAN communication channel. In theembodiment shown in FIG. 2, the second AP 220 selects the client station240 instead of the client station 250 for a directional transmission 260because the client station 250 is located within the busy sector 232-2,while the client station 240 is located in an “idle” sector 232-4 thatis not busy. The second AP 220 generates a PPDU for the transmission tothe client station 240 and transmits the PPDU to the client station 240as a directional transmission that occurs during the first transmission(e.g., during transmission 214 and/or transmission 216).

In an embodiment, the second AP 220 includes sixteen or more antennasand divides the service coverage area 230 into sectors with overlappingantenna pattern for each sector, so that any geographical locationwithin the service coverage area 230 is covered by two sectors. In somescenarios, the second AP 220 supports up to eight stream transmissionsusing the IEEE 802.11ax or IEEE 802.11ac protocol (which have a maximumnumber of spatial streams of eight) in each geographical location (i.e.,using eight antenna pairs per location).

FIG. 3 is a diagram of an example access point 320 configured for fullduplex communication using directional transmissions, according to anembodiment. In other words, the access point 320 is configured totransmit and receive, concurrently, in different sectors. The accesspoint 320 generally corresponds to the second AP 220, in someembodiments. In the embodiment shown in FIG. 3, the access point 320performs a first, directional transmission 340 of a PPDU to the clientstation 250 in the sector 232-2 (i.e., using the antenna 222-2 assignedto the sector 232-2). The access point 320 identifies the sector 232-2as busy while the first, directional transmission is ongoing. The accesspoint 320 selects the client station 240 for a second transmission 350using the identification of the one or more busy sectors (i.e., thesector 232-2 used by the first transmission 340). The secondtransmission 350 is from the client station 240, in an embodiment. Insome embodiments, the first transmission 340 is a first single usertransmission and the second transmission 350 is a second single usertransmission. In other embodiments, the transmission 340 is from theclient station 250 to the access point 320 and the transmission 350 isfrom the access point 320 to the client station 240.

In an embodiment, the access point 320 selects the client station 240because it is located in the sector 232-4 that is furthest away from thebusy sector 232-2. In another embodiment, the access point 320 hasrespective channel estimates corresponding to the WLAN communicationchannel between the access point 320 and its associated client stations.In this embodiment, the access point 320 selects the station that isexpected to introduce less interference to the ongoing transmission 340.

FIG. 4 is a diagram of an example access point 420 configured forparallel communication using directional transmissions, according to anembodiment. In other words, the access point 420 is configured totransmit, concurrently, in different sectors, or to receive,concurrently, in different sectors. The access point 420 generallycorresponds to the second AP 220, in some embodiments. In the embodimentshown in FIG. 4, the access point 420 performs a first, directionaltransmission 440 of a PPDU to the client station 250 in the sector232-2. The access point 420 identifies the sector 232-2 as busy whilethe first, directional transmission 440 is ongoing. The access point 420selects the client station 240 for a second, directional transmission450 using the identification of the one or more busy sectors (i.e., thesector 232-2 used by the first transmission 440). In some embodiments,the first transmission 440 is a first single user transmission and thesecond transmission 450 is a second single user transmission. In otherwords, the first transmission 440 and the second transmission 450 arenot MU-MIMO transmissions because a steering matrix and correspondingnull data packet exchange is not required. Instead, the firsttransmission 440 and the second transmission 450 are orthogonal to eachother based on the directionality of the corresponding antennas. Inother embodiments, the transmission 440 is from the client station 250to the access point 420 and the transmission 450 is from the clientstation 240 to the access point 420.

FIG. 5 is a block diagram of an access point 500 configured for paralleltransmission and/or parallel reception, in an embodiment. The accesspoint 500 generally corresponds to the access point 114 of FIG. 1, butthe network interface device 122 includes two or more PHY processors 530and 540, instead of a single PHY processor 130. The PHY processors 530and 540 generally correspond to the PHY processor 130, but share thesame antennas 138 using a multiplexor 560 or other suitable processor tocontrol access to the antennas (e.g., using a time sharing algorithm).In this way, the access point 500 is equivalent to two separate accesspoints having dynamically shared antennas (e.g., the antennas 138). Inan embodiment, a receiver finite state machine (FSM) of the access point500 is common up until an energy detection (ED) portion, with subsequentportions of the receiver FSM being partitioned into two portions (i.e.,one portion for each of the parallel receptions).

FIG. 6 is an example timing diagram 600 for the second AP 220, which isfurther configured to request a frame exchange for channel estimation,in an embodiment. The second AP 220 is configured to request the frameexchange as a form of cooperative communication with the first AP 210 todetermine i) a first channel estimate of a WLAN communication channelbetween the second AP 220 and the first AP 210, and ii) a second channelestimate of the WLAN communication channel between the second AP 220 andthe client station 214, using measurements at the second AP 220 of theframe exchange, in an embodiment. The frame exchange is between thefirst AP 210 and the client station 214, but the frame exchange istriggered or requested by the second AP 220. In the embodiment shown inFIG. 6, the frame exchange is a request-to-send/clear-to-send (RTS/CTS)frame exchange between the first AP 210 and the first client station214.

The second AP 220 sends a request 610 to the first AP 210 to perform theRTS/CTS frame exchange, in some embodiments. The RTS/CTS frame exchangeis configured for a full sounding, in other words, the frame exchange isconfigured so that i) an RTS frame 620 transmitted by the first AP 210to the client station 214 includes a number of long training fieldscorresponding to a number of antennas of the first AP 210, and ii) a CTSframe 630 transmitted by the client station 214 to the first AP 210includes a number of long training fields corresponding to a number ofantennas of the client station 214. Although the RTS frame 620 and CTSframe 630 are not addressed to the second AP 220, the second AP 220 isconfigured to determine the first channel estimate using, at least inpart, interference 621 from the RTS frame 620 and to determine thesecond channel estimate using, at least in part, interference 631 fromthe CTS frame 630.

Using the first and second channel estimates, the second AP 220 performsbeamforming for a subsequent transmission so that interference with anongoing transmission between the first AP 210 and the client station 214is reduced, in various embodiments. In the embodiment shown in FIG. 6,the first AP 210 and the client station 214 perform a firsttransmission, for example, the first AP 210 transmits a data frame 640to the client station 214. The second AP 220 determines a precodermatrix for a second transmission (e.g., a data frame 650) to the secondclient station 240 as a null space of the first channel estimate and thesecond channel estimate and generates the data frame 650 using theprecoder matrix (e.g., a beamforming matrix).

As an example, where V_(A1A2) is the channel estimate between the firstAP 210 and the second AP 220, and V_(S1A2) is the channel estimatebetween the client station 214 and the second AP 220, then a precodermatrix Q=Null([V_(A1A2) V_(S1A2)]), where Null(A) is the Null space ofthe matrix A. When the precoder matrix Q is available, then there is noconstraint on the transmission link between the second AP 220 and theclient station 240, other than the maximum number of streams availablefor transmission, where the maximum number of streams is the rank of theprecoder matrix Q.

In some scenarios, the precoder matrix Q based on both channel estimatesdoes not exist. In an embodiment, when a rank of the precoder matrix Qis zero, the second AP 220 is configured to determine the precodermatrix Q as the Null space of the channel estimate that corresponds tothe receiver of the other transmission (i.e., the receiver of the dataframe 640: the client station 214). In other words, the second AP 220attempts to null the data frame 650 only at the receiver of the firsttransmission. In this embodiment, the second AP 220 determines theprecoder matrix Q=Null (V_(S1A2)). In this embodiment, where the secondtransmission is not nulled at the first AP 210, the WLAN communicationchannel should be free when the first AP 210 is sensing the channel foran acknowledgment (e.g., ACK 660). In an embodiment, the second AP 220generates the data frame 650 to have an end time on or before an endtime of the first transmission (e.g., an end of the data frame 640). Inthis embodiment, the data frame 650 does not interfere with theacknowledgment frame 660 of the data frame 640. In an embodiment, thesecond AP 220 determines a length of the first transmission 640 andgenerates the second transmission 650 to have a suitable length. In thisembodiment, the second transmission of the data frame 650 is unprotectedin that an immediate acknowledgment is not possible because it wouldcollide with the acknowledgment 660.

In some embodiments, the second AP 220 requests a suitable frameexchange other than the RTS/CTS frame exchange. In an embodiment, forexample, the second AP 220 sends a null data packet having a request forfeedback for a multi-user transmission, where the multi-user clientstations are the first AP 210, the client station 214, and the clientstation 240. In this embodiment, the second AP 220 determines i) a firstchannel estimate of the WLAN communication channel between the second AP220 and the first AP 210, and ii) a second channel estimate of the WLANcommunication channel between the second AP 220 and the client station214, using measurements at the first AP 210 of a first null data packettransmitted from the second AP 220 to the first AP 210 and usingmeasurements at the first client station 214 of a second null data frametransmitted from the second AP 220 to the first client station 214. Inthis embodiment, the first AP 210 is configured to respond to the firstnull data frame as a client station would be expected to respond, i.e.,by performing a channel estimate and transmitting a feedback frame thatindicates the channel estimate to the second AP 220.

FIG. 7 is a flow diagram illustrating an example method 700 fortransmitting a first physical layer (PHY) protocol data unit (PPDU) in awireless local area network (WLAN) communication channel, in anembodiment. In an embodiment, the method 700 is implemented by an accesspoint in the WLAN, according to an embodiment. With reference to FIG. 1,the method 700 is implemented by the network interface 122, in anembodiment. For example, in one such embodiment, the PHY processor 130is configured to implement the method 700. According to anotherembodiment, the MAC processor 126 is also configured to implement atleast a part of the method 700. With continued reference to FIG. 1, inyet another embodiment, the method 700 is implemented by the networkinterface 162 (e.g., the PHY processor 170 and/or the MAC processor166). In other embodiments, the method 700 is implemented by othersuitable network interfaces.

At block 702, one or more sectors of a service coverage area of thefirst communication device are identified, where the one or moreidentified sectors are busy with a first transmission over the WLANcommunication channel, in an embodiment. In one embodiment, the one ormore sectors correspond to the sectors 232-2 and 232-3 of FIG. 2. Inanother embodiment, the one or more sectors correspond to the sector232-2 of FIG. 3. In yet another embodiment, the one or more sectorscorrespond to the sector 232-2 of FIG. 4. In some embodiments, thesector controller 132 of the network interface 122 (FIG. 1) identifiesthe busy sectors. In an embodiment, the carrier sense component 133identifies the busy sectors.

At block 704, a second communication device is selected to receive thefirst PPDU during a second, directional transmission that at leastpartially temporally overlaps a duration of the first transmission usingthe identification of the one or more busy sectors, in an embodiment. Inone embodiment, the second communication device is the client station240 of FIG. 2. In another embodiment, the second communication device isthe client station 240 of FIG. 3. In yet another embodiment, the secondcommunication device is the client station 240 of FIG. 4. In someembodiments, the sector controller 132 selects the second communicationdevice using the identification of the busy sectors from the carriersense component 133.

At block 706, the first PPDU is generated for transmission to the secondcommunication device, in an embodiment. In one embodiment, the firstPPDU is the PPDU 260 of FIG. 2. In another embodiment, the first PPDU isthe PPDU 350 of FIG. 3. In yet another embodiment, the PPDU is the PPDU450 of FIG. 4.

At block 708, the first PPDU to the second communication device istransmitted as the second, directional transmission during the firsttransmission. In various embodiments, the second, directionaltransmission at least partially temporally overlaps the firsttransmission. In an embodiment, for example, the second, directionaltransmission begins during the first transmission and endssimultaneously with an end of the first transmission. In anotherembodiment, for example, the second, directional transmission beginsduring the first transmission and ends before the end of the firsttransmission. In some embodiments, the transceiver 134 generates andtransmit the first PPDU.

Further aspects of the present invention relate to one or more of thefollowing clauses.

In an embodiment, a method for transmitting a first physical layer (PHY)protocol data unit (PPDU) in a wireless local area network (WLAN)communication channel includes: identifying, at a first communicationdevice, one or more sectors of a service coverage area of the firstcommunication device that are busy with a first transmission over theWLAN communication channel; selecting, at the first communication deviceand using the identification of the one or more busy sectors, a secondcommunication device to receive the first PPDU during a second,directional transmission that at least partially temporally overlaps aduration of the first transmission; generating, at the firstcommunication device, the first PPDU for transmission to the secondcommunication device; and transmitting, at the first communicationdevice, the first PPDU to the second communication device as the second,directional transmission during the first transmission.

In other embodiments, the method includes any suitable combination ofone or more of the following features.

The method further includes maintaining, at the first communicationdevice, respective target lists of sectors of the service coverage areain which respective ones of communication devices associated with thefirst communication device are estimated to be located.

The first communication device has a plurality of antennas, ones of theplurality of antennas being configured to transmit in particular sectorsof the service coverage area. Transmitting the first PPDU to the secondcommunication device during the first transmission includes transmittingthe first PPDU using antennas of the plurality of antennas that areconfigured to directionally transmit in sectors of the target list ofsectors that corresponds to the second communication device.

Maintaining the respective target lists of sectors includes identifying,at the first communication device, sectors in which the secondcommunication device is estimated to be located and storing theidentified sectors in a target list that corresponds to the secondcommunication device.

Maintaining the respective target lists of sectors includes updating thetarget list that corresponds to the second communication device based ona reception of a second PPDU having a non-null data portion.

Identifying the one or more sectors of the service coverage area of thefirst communication device that are busy includes identifying the one ormore sectors as busy when the first transmission is between a thirdcommunication device and a fourth communication device.

The method further includes determining i) a first channel estimate ofthe WLAN communication channel between the first communication deviceand the third communication device, and ii) a second channel estimate ofthe WLAN communication channel between the first communication deviceand the fourth communication device, using measurements at the firstcommunication device of a frame exchange between the third and fourthcommunication devices.

Determining the first channel estimate and the second channel estimateincludes determining the first channel estimate and the second channelestimate using measurements at the first communication device of i) arequest to send (RTS) frame transmitted by the third communicationdevice to the fourth communication device, the RTS frame having a numberof long training fields corresponding to a number of antennas of thethird communication device, and ii) a clear to send (CTS) frametransmitted by the fourth communication device to the thirdcommunication device in response to the RTS frame, the CTS frame havinga number of long training fields corresponding to a number of antennasof the fourth communication device.

The method further includes transmitting, by the first communicationdevice, a request to the third communication device to perform the frameexchange between the third and fourth communication devices.

Generating the first PPDU includes: determining, at the firstcommunication device, a precoder matrix for the second transmission as anull space of the first channel estimate and the second channelestimate; and generating the first PPDU using the precoder matrix.

Generating the first PPDU includes: determining, at the firstcommunication device, a precoder matrix for the second transmission as anull space of a channel estimate that corresponds to a receiver of thefirst transmission; and generating the first PPDU using the precodermatrix.

Generating the first PPDU includes generating the first PPDU to have anend time on or before an end of the first transmission.

The method further includes determining i) a first channel estimate ofthe WLAN communication channel between the first communication deviceand the third communication device, and ii) a second channel estimate ofthe WLAN communication channel between the first communication deviceand the fourth communication device, using measurements at the thirdcommunication device of a first null data frame transmitted from thefirst communication device to the third communication device and usingmeasurements at the fourth communication device of a second null datapacket transmitted from the first communication device to the fourthcommunication device, wherein the first communication device and one ofthe third and fourth communication devices are access points.

Identifying the one or more sectors that are busy includes identifying asector as busy when the first transmission is from the firstcommunication device to a third communication device that is located inthe sector.

The first transmission is a first single user transmission andtransmitting the first PPDU to the second communication device is asecond single user transmission.

Identifying the one or more sectors that are busy includes identifying asector as busy when the first communication device is receiving thefirst transmission from a third communication device that is located inthe sector.

The first communication device includes a directional antenna configuredfor transmission to a sector in which the second communication device islocated and transmitting the first PPDU to the second communicationdevice includes transmitting the first PPDU using the directionalantenna.

The first communication device includes a plurality of antennasconfigured for a single user beamforming transmission to a sector inwhich the second communication device is located and transmitting thefirst PPDU to the second communication device includes transmitting thefirst PPDU as a single user beamforming transmission using the pluralityof antennas.

The method further includes dividing, at the first communication device,the service coverage area into a plurality of sectors. Identifying theone or more sectors that are busy includes performing a separate carriersense procedure for each sector of the plurality of sectors.

The first communication device includes a plurality of antennas, and themethod further includes assigning ones of the antennas to ones of theplurality of sectors.

In another embodiment, an apparatus for transmitting a first PPDU in aWLAN communication channel includes a network interface device havingone or more integrated circuits. The one or more integrated circuitsinclude a sector controller configured to identify one or more sectorsof a service coverage area of a first communication device that are busywith a first transmission over the WLAN communication channel. Thesector controller is further configured to select, using theidentification of the one or more busy sectors, a second communicationdevice to receive the first PPDU during a second, directionaltransmission that at least partially temporally overlaps a duration ofthe first transmission. The one or more integrated circuits areconfigured to generate the first PPDU for transmission to the secondcommunication device. The one or more integrated circuits are configuredto transmit the first PPDU to the second communication device as thesecond, directional transmission during the first transmission.

In other embodiments, the apparatus includes any suitable combination ofone or more of the following features.

The one or more integrated circuits are configured to maintainrespective target lists of sectors of the service coverage area in whichrespective ones of communication devices associated with the firstcommunication device are estimated to be located.

The first communication device has a plurality of antennas, ones of theplurality of antennas being configured to transmit in particular sectorsof the service coverage area. The one or more integrated circuits areconfigured to transmit the first PPDU using antennas of the plurality ofantennas that are configured to directionally transmit in sectors of thetarget list of sectors that corresponds to the second communicationdevice.

The one or more integrated circuits are configured to identify, at thefirst communication device, sectors in which the second communicationdevice is estimated to be located and store the identified sectors in atarget list that corresponds to the second communication device.

The one or more integrated circuits are configured to update the targetlist that corresponds to the second communication device based on areception of a second PPDU having a non-null data portion.

The one or more integrated circuits are configured to identify the oneor more sectors as busy when the first transmission is between a thirdcommunication device and a fourth communication device.

The one or more integrated circuits are configured to determine i) afirst channel estimate of the WLAN communication channel between thefirst communication device and the third communication device, and ii) asecond channel estimate of the WLAN communication channel between thefirst communication device and the fourth communication device, usingmeasurements at the first communication device of a frame exchangebetween the third and fourth communication devices.

The one or more integrated circuits are configured to determine thefirst channel estimate and the second channel estimate usingmeasurements at the first communication device of i) a request to send(RTS) frame transmitted by the third communication device to the fourthcommunication device, the RTS frame having a number of long trainingfields corresponding to a number of antennas of the third communicationdevice, and ii) a clear to send (CTS) frame transmitted by the fourthcommunication device to the third communication device in response tothe RTS frame, the CTS frame having a number of long training fieldscorresponding to a number of antennas of the fourth communicationdevice.

The one or more integrated circuits are configured to transmit, by thefirst communication device, a request to the third communication deviceto perform the frame exchange between the third and fourth communicationdevices.

The one or more integrated circuits are configured to determine, at thefirst communication device, a precoder matrix for the secondtransmission as a null space of the first channel estimate and thesecond channel estimate, and generate the first PPDU using the precodermatrix.

The one or more integrated circuits are configured to determine, at thefirst communication device, a precoder matrix for the secondtransmission as a null space of a channel estimate that corresponds to areceiver of the first transmission; and generate the first PPDU usingthe precoder matrix.

The one or more integrated circuits are configured to generate the firstPPDU to have an end time on or before an end of the first transmission.

The one or more integrated circuits are configured to determine i) afirst channel estimate of the WLAN communication channel between thefirst communication device and the third communication device, and ii) asecond channel estimate of the WLAN communication channel between thefirst communication device and the fourth communication device, usingmeasurements at the third communication device of a first null dataframe transmitted from the first communication device to the thirdcommunication device and using measurements at the fourth communicationdevice of a second null data packet transmitted from the firstcommunication device to the fourth communication device, wherein thefirst communication device and one of the third and fourth communicationdevices are access points.

The one or more integrated circuits are configured to identify a sectoras busy when the first transmission is from the first communicationdevice to a third communication device that is located in the sector.

The first transmission is a first single user transmission andtransmitting the first PPDU to the second communication device is asecond single user transmission.

The one or more integrated circuits are configured to identify a sectoras busy when the first communication device is receiving the firsttransmission from a third communication device that is located in thesector.

The first communication device includes a directional antenna configuredfor transmission to a sector in which the second communication device islocated and the one or more integrated circuits are configured totransmit the first PPDU using the directional antenna.

The first communication device includes a plurality of antennasconfigured for a single user beamforming transmission to a sector inwhich the second communication device is located and the one or moreintegrated circuits are configured to transmit the first PPDU as asingle user beamforming transmission using the plurality of antennas.

The one or more integrated circuits are configured to divide, at thefirst communication device, the service coverage area into a pluralityof sectors, and perform a separate carrier sense procedure for eachsector of the plurality of sectors.

The first communication device comprises a plurality of antennas, andthe one or more integrated circuits are configured to assign ones of theantennas to ones of the plurality of sectors.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. The software or firmware instructions mayinclude machine readable instructions that, when executed by one or moreprocessors, cause the one or more processors to perform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for transmitting a first physical layer(PHY) protocol data unit (PPDU) in a wireless local area network (WLAN)communication channel, the method comprising: determining, at a firstcommunication device, i) a first channel estimate of the WLANcommunication channel between the first communication device and a thirdcommunication device, and ii) a second channel estimate of the WLANcommunication channel between the first communication device and afourth communication device, using measurements at the firstcommunication device of a frame exchange between the third and fourthcommunication devices; determining, at the first communication device,that at least a portion of a service coverage area of the firstcommunication device is busy with a first transmission between the thirdcommunication device and the fourth communication device over the WLANcommunication channel; selecting, at the first communication device, asecond communication device to receive the first PPDU during a second,directional transmission that at least partially temporally overlaps aduration of the first transmission; generating, at the firstcommunication device, the first PPDU for transmission to the secondcommunication device, including determining a precoder matrix for thesecond transmission based on the first channel estimate and the secondchannel estimate, and generating the first PPDU using the precodermatrix; and transmitting, at the first communication device, the firstPPDU to the second communication device as the second, directionaltransmission during the first transmission.
 2. The method of claim 1,further comprising: maintaining, at the first communication device,respective target lists of sectors of the service coverage area in whichrespective ones of communication devices associated with the firstcommunication device are estimated to be located.
 3. The method of claim2, wherein: the first communication device has a plurality of antennas,ones of the plurality of antennas being configured to transmit inparticular sectors of the service coverage area; and transmitting thefirst PPDU to the second communication device during the firsttransmission comprises transmitting the first PPDU using antennas of theplurality of antennas that are configured to directionally transmit insectors of the target list of sectors that corresponds to the secondcommunication device.
 4. The method of claim 2, wherein maintaining therespective target lists of sectors comprises identifying, at the firstcommunication device, sectors in which the second communication deviceis estimated to be located and storing the identified sectors in atarget list that corresponds to the second communication device.
 5. Themethod of claim 2, wherein maintaining the respective target lists ofsectors comprises: updating the target list that corresponds to thesecond communication device based on a reception of a second PPDU havinga non-null data portion.
 6. The method of claim 1, wherein determiningthe first channel estimate and the second channel estimate comprisesdetermining the first channel estimate and the second channel estimateusing measurements at the first communication device of i) a request tosend (RTS) frame transmitted by the third communication device to thefourth communication device, the RTS frame having a number of longtraining fields corresponding to a number of antennas of the thirdcommunication device, and ii) a clear to send (CTS) frame transmitted bythe fourth communication device to the third communication device inresponse to the RTS frame, the CTS frame having a number of longtraining fields corresponding to a number of antennas of the fourthcommunication device.
 7. The method of claim 1, further comprisingtransmitting, by the first communication device, a request to the thirdcommunication device to perform the frame exchange between the third andfourth communication devices.
 8. The method of claim 1, whereindetermining the precoder matrix for the second transmission comprisesdetermining the precoder matrix as a null space of the first channelestimate and the second channel estimate.
 9. The method of claim 1,wherein determining the precoder matrix for the second transmissioncomprises determining the precoder matrix as a null space of a channelestimate that corresponds to a receiver of the first transmission. 10.The method of claim 1, wherein generating the first PPDU comprisesgenerating the first PPDU to have an end time on or before an end of thefirst transmission.
 11. The method of claim 1, wherein the firstcommunication device includes a directional antenna configured fortransmission to a sector in which the second communication device islocated and transmitting the first PPDU to the second communicationdevice comprises transmitting the first PPDU using the directionalantenna.
 12. The method of claim 1, wherein the first communicationdevice includes a plurality of antennas configured for a single userbeamforming transmission to a sector in which the second communicationdevice is located and transmitting the first PPDU to the secondcommunication device comprises transmitting the first PPDU as a singleuser beamforming transmission using the plurality of antennas.
 13. Themethod of claim 1, further comprising dividing, at the firstcommunication device, the service coverage area into a plurality ofsectors; wherein determining that at least a portion of a servicecoverage area is busy comprises performing a separate carrier senseprocedure for each sector of the plurality of sectors.
 14. The method ofclaim 13, wherein the first communication device comprises a pluralityof antennas, the method further comprising assigning ones of theplurality of antennas to ones of the plurality of sectors.
 15. A methodfor transmitting a first physical layer (PHY) protocol data unit (PPDU)in a wireless local area network (WLAN) communication channel, themethod comprising: determining, at the first communication device, i) afirst channel estimate of the WLAN communication channel between thefirst communication device and a third communication device, and ii) asecond channel estimate of the WLAN communication channel between thefirst communication device and a fourth communication device, usingmeasurements at the third communication device of a first null dataframe transmitted from the first communication device to the thirdcommunication device and using measurements at the fourth communicationdevice of a second null data packet transmitted from the firstcommunication device to the fourth communication device, wherein thefirst communication device and one of the third and fourth communicationdevices are access points; determining, at the first communicationdevice, that at least a portion of a service coverage area of the firstcommunication device is busy with a first transmission between the thirdcommunication device and the fourth communication device over the WLANcommunication channel; selecting, at the first communication device, asecond communication device to receive the first PPDU during a second,directional transmission that at least partially temporally overlaps aduration of the first transmission; generating, at the firstcommunication device, the first PPDU for transmission to the secondcommunication device, including determining a precoder matrix for thesecond transmission based on the first channel estimate and the secondchannel estimate, and generating the first PPDU using the precodermatrix; and transmitting, at the first communication device, the firstPPDU to the second communication device as the second, directionaltransmission during the first transmission.